The present invention relates to a loadbearing structure for heavy vehicles, e.g. a freight vehicle, and to a process for manufacturing a loadbearing structure for heavy vehicles.
A known practice for heavy vehicles, e.g. trucks and similar freight vehicles, is to design a loadbearing structure in the form of a vehicle frame. The commonest type of vehicle frame for freight vehicles is a ladder type of frame member structure which incorporates a pair of parallel longitudinal side members. These side members extend substantially along the whole length of the vehicle, on opposite sides of the vehicle. Along the whole length of the side members a multiplicity of transverse members are arranged at intervals and connect the side members to one another. Such a frame member structure supports the driving cab and a load surface, e.g. a load platform or fixed van superstructure. The frame member structure also caters for fitting various components of the vehicle, e.g. engine, suspension system, wheel shafts etc.
A loadbearing structure in the form of a frame structure for a heavy vehicle serves as the main loadbearing element for achieving strength and rigidity, unlike buses, for example, in which the whole of the bodywork affects their rigidity and strength. However, a traditional form of vehicle frame is designed to be relatively bendable and twistable (herein called torsionable), with the object of being able to cope with heavy loads and varying road conditions, ranging from forest roads or no roads at all to smooth motorways. However, this relatively low resistance to bending and twisting entails difficulties as regards the vehicle""s running characteristics. It is also difficult on a torsionable vehicle frame to try to compensate for the vehicle""s moderate running characteristics by installing some kind of sophisticated suspension system. As transport by heavy vehicles currently takes place largely on smooth roads and decreasingly on uneven forest roads and the like, better running characteristics on the latter have become increasingly important. Frame rigidity greatly influences the running characteristics. On a smooth road the running characteristics can be improved by increasing the rigidity of the frame.
When a heavy vehicle with a ladder type of frame member structure has to be equipped with a load surface in the form of a load platform or permanent van superstructure, it is usual for U-shaped members to be arranged at the bottom of the frame member structure to render the frame member structure rigid and provide support for the platform or van body relative to the frame members. This causes problems in that a built-on platform or van body is relatively rigid, whereas the frame member structure is torsionable, which means that special fastenings are required. U-shaped members for load platforms/van bodies cause an undesirable extra vehicle weight increase.
WO-A2-9414627 describes a loadbearing structure in the form of a vehicle frame for a motor vehicle, which incorporates a tubular extruded section designed to allow optimum utilisation of the space in the vehicle body. The tubular extruded section is used to accommodate such items as batteries, which are inserted into it by means of trolleys. The structure according to WO-A2-9414627 does not indicate any solution to the problems described with regard to the above state of the art.
The object of the present invention is to provide a loadbearing structure for vehicles, preferably heavy trucks, which is significantly more rigid than conventional structures and obviates said disadvantages of the state of the art. One object is therefore to provide a structure which results in better vehicle running characteristics in the most commonly occurring operating situations, which in the case of heavy trucks is relatively smooth roads. A further object is to provide a weight-optimised structure which is easy and inexpensive to manufacture. Another object of the present invention is to provide a structure which makes it easy to carry out repairs and servicing both of the frame and of components arranged on it, and to provide a large proportion of said components with an environment protected against external influences.
To these ends, the invention is a loadbearing structure for heavy vehicles, e.g. a freight vehicle, which incorporates a box-shaped hollow unit extending in the longitudinal direction of the vehicle. Wall elements of thin wall thickness are connected to one another to form the box-shaped unit. The invention provides a loadbearing structure for heavy vehicles which is many times more rigid than conventional structures but is nevertheless of relatively low weight and is relatively easy and inexpensive to manufacture. The present invention also relates to a process for manufacturing such a loadbearing structure for heavy vehicles.
An advantage of the solution according to the invention is that it makes possible a very torsion-resistant structure with low weight, resulting in better running characteristics, comfort and road holding as compared with structures according to the state of the art. It improves rigidity in all directions, but particularly the torsional rigidity. The loadbearing structure according to the present invention can increase the torsional rigidity of the vehicle frame by several thousand times and the bending resistance by about ten times. All the constituent elements of the structure participate in the distribution of forces and increase the rigidity. The structure according to the present invention also makes it possible to achieve a weight-optimised vehicle frame. It also facilitates repair and servicing work through good accessibility from the underside of the vehicle.
The box-shaped body is advantageously bounded by an upper roof wall element arranged horizontally, a lower bottom wall element and two vertical wall elements. The respective vertical wall elements and part of the horizontal wall element may advantageously be manufactured and designed integrally. This makes it possible to create mutually identical composite sections which are stackable and which also render the manufacturing process easier and more efficient. Two such separate elements which in certain cases are identical can be brought together at assembly stage to form a composite unit with vertical walls and a horizontal upper wall element. The respective vertical wall elements may thus advantageously be designed with a wall portion arranged substantially vertically which also incorporates part of a horizontal wall element extending from the upper end of the vertical wall element. The wall element thus forms an L-shape. Two opposite L-shaped wall elements placed at a distance from one another are joined together by the two respective protruding horizontal portions and form in combination with one another a composite unit incorporating the upper horizontal wall element and the vertical wall elements.
The wall elements for the box-shaped structure may preferably be in sheet form and largely consist of corrugated sheetmetal, which is much more rigid than entirely planar sheetmetal of the same thickness. The wall elements consist of material with thin wall thickness with a view to achieving a weight-optimised loadbearing structure. For application on a heavy freight vehicle, the material thickness in the case of sheet steel may be about 5 mm or less.
According to one embodiment, the box-shaped unit is provided internally with at least one supporting frame structure. The purpose of such a supporting frame is to reduce the risk of buckling of the constituent wall elements of the box-shaped unit. Advantageously, supporting frame structures are placed within and distributed along the whole of the box-shaped unit. The larger the number of supporting frames used in the box-shaped unit, the higher the torsional rigidity of the resulting structure. On the inside of the box-shaped unit, the respective supporting frame structures are firmly connected to the wall elements. Each supporting frame structure is a homogeneous frame, advantageously integral, which has a substantially square shape and a central aperture. The supporting frame incorporates an upper and a lower horizontal element and, arranged between them, two substantially vertical elements at a distance from one another. The supporting frame may also have other suitable geometrical shapes, e.g. rectangular or parallelepipedic. The thickness and extent of the supporting frame in the longitudinal direction of the box frame are small relative to the latter""s extent in the width and height directions, i.e. transverse to the extent of the box-shaped unit in the longitudinal direction.
According to another embodiment, the loadbearing structure incorporates supporting devices arranged on the outside of the substantially vertical wall elements of the box-shaped unit. These supporting devices are advantageously placed in the longitudinal direction on the outside and distributed along substantially the whole of the box-shaped unit. The supporting devices have advantageously in the vertical plane an extent which corresponds to the vertical plane for a supporting frame and serve primarily as supports for the sheetmetal panels which constitute the vehicle""s load surface.
The loadbearing structure has a load surface arranged on its top side. The upper horizontal wall element may preferably consist of corrugated sheetmetal which, according to a further embodiment, may have a planar panel arranged permanently on its top side. The result is a structure with great shear resistance which at the same time provides a load surface on the top of the panel. Such a panel may be of metallic material such as aluminium or, for example, wooden material such as plywood.
In accordance with the process for manufacture of a loadbearing structure for heavy vehicles according to the present invention, the constituent wall elements of the box-shaped unit are made of thin sheetmetal material. The wall elements may have dividing lines in both the transverse and longitudinal directions of the vehicle and be fastened along them at every second one to form a torsion-resistant box-shaped unit. The wall elements may be manufactured by a simple rolled forming process or by rolling mill forming. Said load surface, preferably made of corrugated sheet steel, may also be manufactured by rolled forming.
According to a preferred embodiment, the assembly of the loadbearing structure according to the present invention involves first fitting one or, advantageously, a multiplicity of supporting frame structures to the bottom wall element. Thereafter, suspension devices and other vehicle components which are to form part of the box-shaped unit are fitted to the supporting frame structures before the L-shaped elements are fastened to the supporting frame structures to form the box-shaped unit. Thereafter, preassembled vehicle components such as wheel shafts, gearbox, engine and cab body are fitted to the suspension devices before the supporting devices and their load surface are fitted. Manufacture may take place in large sections and in modules which substantially simplify assembly and disassembly. When components in the box-shaped unit have to be serviced or repaired, only a bottom wall element need be removed.